Tactical radio communications rely heavily on ad-hoc mobile radio networks and systems. Emerging tactical battlefield networks typically include a collection of autonomous host nodes or terminals that are mobile. These nodes move into and out of radio communication range with each other, and generally can not rely on a pre-defined fixed infrastructure within their environment. The nodes in an ad-hoc communications network may move, be destroyed, or new nodes may join the network. In other words, the network environment is mobile, wireless, dynamically changing, and is “infrastructure-less.”
Wireless Ad-hoc Networks
In a wireless ad-hoc network a group of autonomous nodes or terminals communicate with each other by forming a multi-hop radio network and maintaining connectivity in a decentralized manner. The nodes represent radio communication devices which may be with a person (such as a warfighter), a ground or an air vehicles platforms, an Unmanned Air Vehicle (UAV), or an Unmanned Ground Vehicles (UGV), etc. The network can be represented by a graph, where the graph vertices are the network nodes and two vertices are connected by an edge if the corresponding nodes can be reached (or communicate) by a radio link. In other words the nodes can be depicted as a set of points. Connections between these points can be shown as lines with each line representing a radio link over which one node can communicate with another node. Two radio nodes are said to be communicating if the link quality is above a predefined threshold, such as, if the signal-to-noise ratio is above a predefined threshold.
The mobile nodes must be able to communicate with each other over a wireless media without any infra-structured network component support such as fixed radio relay base stations. Each mobile node can typically communicate with its neighboring mobile nodes which are a single radio hop away. Each mobile node operates not only as a host but also as a router, forwarding packets of information to other mobile nodes in the network that may not be within direct wireless transmission range of each other. Each node participates in an ad-hoc routing protocol that allows it to discover “multi-hop” paths through the network to any other node. Control of the network is distributed among the nodes.
The network topology is “ad-hoc” in that it dynamically changes over time because the connectivity among the nodes may vary with time. For example, because the nodes are mobile, the network topology may change rapidly and unpredictably over time due to node departures, new node arrivals, and the mobility of the nodes. Nodes can fail, for example, if they are destroyed or due to hard or soft failures which occur in the battlefield. Moreover, since the nodes communicate over wireless links, the nodes have to contend with the effects of radio communication, such as noise, fading, and interference. Factors such as variable wireless link quality, propagation path loss, fading, multi-user interference, power expended, and topological changes may become relevant issues. Connections between nodes may also be broken or established due to, for example, distance factors, variations in signal strength, weather, mountains, buildings, loss of node, etc. Thus, changes in propagation conditions and the environment, as well as the unpredictability of node movements and sporadic node failures, can contribute to the dynamic nature of an ad-hoc network. These problems are even further complicated in a military environment where the preservation of security, latency, reliability, intentional jamming, and recovery from failure are significant concerns.
Accordingly, one of the most important features of any an ad-hoc mobile network, is the ability to adapt well to link changes, namely changes in the interconnectivity between mobile nodes.
Joint Tactical Radio System (JTRS)
The Joint Tactical Radio System (JTRS) is a Department of Defense (DoD) initiative designed to provide a flexible new approach to meet diverse warfighter communications needs through software-programmable tactical radio technology or “software defined radios (SDRs).” It is desirable to provide SDRs which can provide a warfighter with voice, data and video communications across a battlespace. Beyond the battlefield, JTRS holds great potential for initiatives such as homeland security, federal, state and local law enforcement, search and rescue, commercial aviation and international commercial applications. The JTRS implements the concept of relay and translation nodes (land, sea, air and space based) to help ensure that tactical users can access required information no matter where it resides.
There are several issues facing dynamic ad-hoc networks. For example, links between nodes are the frequently broken as nodes move or are destroyed. In addition, nodes can randomly fail due to enemy or unintentional attacks.
Thus, a challenge in ad-hoc networks is to maintain network-wide connectivity. In this context a network is “connected” if there is a communication path, either node-to-node or by multiple-node-hopping, which can allow any two nodes in the network to communicate with one another. As noted above, as nodes move the links between the nodes can be broken and the network can partition into isolated sub-networks. A break in the network can create a situation where the node cannot communicate with another node (absolutely no paths). In this case, the network is said to be “partitioned.”
In ad-hoc radio networks, there is a need for techniques which can assist with battle space communication planning and fault management sub-systems to help ensure communication reliability and connectivity of the ad-hoc network. It would be desirable to provide techniques for use during the planning stage of a mission to predict and detect link failures, determine and identify network partitions, and assess the reliability of the network. It would also be desirable to provide techniques for restoring connectivity to a partitioned ad-hoc network so that each node can communicate with other nodes. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.